Smith Jeffrey A, Maloney David J, Hecht Sidney M, Lannigan Deborah A
Center for Cell Signaling, Department of Pathology, University of Virginia, Charlottesville, VA 22908, USA.
Bioorg Med Chem. 2007 Jul 15;15(14):5018-34. doi: 10.1016/j.bmc.2007.03.087. Epub 2007 Apr 2.
Inappropriate activity of p90 ribosomal S6 kinase (RSK) has been implicated in various human cancers as well as other pathologies. We previously reported the isolation, characterization, and synthesis of the natural product kaempferol 3-O-(3'',4''-di-O-acetyl-alpha-l-rhamnopyranoside), termed SL0101 [Smith, J. A.; Poteet-Smith, C. E.; Xu, Y.; Errington, T. M.; Hecht, S. M.; Lannigan, D. A. Cancer Res., 2005, 65, 1027-1034: Xu, Y.-M; Smith, J. A.; Lannigan, D. A.; Hecht, S. M. Bioorg. Med. Chem., 2006, 14, 3974-3977: Maloney, D. J.; Hecht, S. M. Org. Lett., 2005, 7, 1097-1099]. SL0101 is a potent and specific inhibitor of RSK; therefore, we performed an analysis of the structural basis for the inhibitory activity of this lead compound. In in vitro kinase assays we found that acylation of the rhamnose moiety and the 4', 5, and 7-hydroxyl groups are responsible for maintaining a high affinity interaction of RSK with SL0101. It is likely that the hydroxyl groups facilitate RSK binding through their ability to form hydrogen bonds. To determine whether the SL0101 derivatives were specific for inhibition of RSK we analyzed their ability to preferentially inhibit the growth of the human breast cancer line, MCF-7, compared to the normal human breast line, MCF-10A. We have previously validated this differential growth assay as a convenient readout for analyzing the specificity of RSK inhibitors [Smith, J. A.; Maloney, D. J.; Clark, D. E.; Xu, Y.-M.; Hecht, S. M.; Lannigan, D. A. Bioorg. Med. Chem., 2006, 14, 6034-6042]. We found that acylation of the rhamnose moiety was essential for maintaining the selectivity for RSK inhibition in intact cells. Further, the efficacy of SL0101 in intact cells is limited by cellular uptake as well as possible hydrolysis of the acetyl groups on the rhamnose moiety by ubiquitous intracellular esterases. These studies should facilitate the development of a RSK inhibitor, based on the SL0101 pharmacophore, as an anti-cancer chemotherapeutic agent.
p90核糖体S6激酶（RSK）的异常活性与多种人类癌症以及其他病理状况有关。我们之前报道了天然产物山奈酚3 - O -（3''，4'' - 二 - O - 乙酰基 - α - L - 鼠李糖苷）的分离、表征及合成，将其命名为SL0101[史密斯，J.A.；波蒂特 - 史密斯，C.E.；徐，Y.；埃林顿，T.M.；赫克特，S.M.；兰尼根，D.A.《癌症研究》，2005年，65卷，1027 - 1034页：徐，Y.-M；史密斯，J.A.；兰尼根，D.A.；赫克特，S.M.《生物有机与药物化学》，2006年，14卷，3974 - 3977页：马洛尼，D.J.；赫克特，S.M.《有机快报》，2005年，7卷，1097 - 1099页]。SL0101是一种强效且特异性的RSK抑制剂；因此，我们对这种先导化合物的抑制活性的结构基础进行了分析。在体外激酶测定中，我们发现鼠李糖部分以及4'、5和7 - 羟基的酰化作用负责维持RSK与SL0101的高亲和力相互作用。羟基很可能通过其形成氢键的能力促进RSK的结合。为了确定SL0101衍生物是否对RSK抑制具有特异性，我们分析了它们相对于正常人乳腺细胞系MCF - 10A优先抑制人乳腺癌细胞系MCF - 7生长的能力。我们之前已经验证了这种差异生长测定法可作为分析RSK抑制剂特异性的便捷读数[史密斯，J.A.；马洛尼，D.J.；克拉克，D.E.；徐，Y.-M.；赫克特，S.M.；兰尼根，D.A.《生物有机与药物化学》，2006年，14卷，6034 - 6042页]。我们发现鼠李糖部分的酰化对于维持完整细胞中RSK抑制的选择性至关重要。此外，SL0101在完整细胞中的功效受到细胞摄取以及鼠李糖部分上的乙酰基可能被普遍存在的细胞内酯酶水解的限制。这些研究应有助于基于SL0101药效团开发一种RSK抑制剂作为抗癌化疗药物。
